Family Tetramelaceae

Tetramelaceae (Warb.) Airy Shaw

~ Datiscaceae

Habit and leaf form. Large, often buttressed trees. Mesophytic. Leaves alternate; petiolate; non-sheathing; simple. Lamina entire; ovate; palmately veined; cross-venulate; cordate. Leaves exstipulate. Lamina margins entire, or dentate. Leaves without a persistent basal meristem.

Leaf anatomy. Stomata present; anomocytic.

Lamina dorsiventral. The mesophyll with sclerencymatous idioblasts (at least in Octomeles). Minor leaf veins without phloem transfer cells (Tetrameles).

Stem anatomy. Cork cambium present; initially superficial. Secondary thickening developing from a conventional cambial ring. Vessel end-walls simple. Wood partially storied (VPI); parenchyma paratracheal.

Reproductive type, pollination. Plants dioecious. Female flowers without staminodes.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in spikes and in panicles. Inflorescences terminal, or axillary; terminal panicles or axillary, solitary spikes. Flowers regular to somewhat irregular; cyclic. Free hypanthium present (the corolla inserted on the calyx).

Perianth with distinct calyx and corolla, or sepaline; 4, or 12–16; 1 whorled, or 2 whorled; isomerous. Calyx 4, or 6–8; 1 whorled; gamosepalous; unequal but not bilabiate, or regular; valvate. Corolla when present, 6–8; 1 whorled; polypetalous; valvate.

Androecium 4, or 6–8. Androecial members free of the perianth; free of one another; 1 whorled. Androecium exclusively of fertile stamens (in the male flowers). Stamens 4, or 6–8; isomerous with the perianth. Anthers dorsifixed; dehiscing via longitudinal slits; extrorse; bilocular. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 4 carpelled, or 6–8 carpelled. Carpels isomerous with the perianth. The pistil 1 celled. Gynoecium syncarpous; synovarious; inferior. Ovary 1 locular. Gynoecium stylate. Styles 4, or 6–8; free; apical. Placentation parietal. Ovules in the single cavity 20–100 (‘many’); pendulous to horizontal; anatropous; bitegmic.

Fruit non-fleshy; dehiscent; a capsule. Capsules valvular. Fruit 20–100 seeded (‘many’). Seeds scantily endospermic, or non-endospermic (?); minute. Embryo straight.

Peculiar feature. The young, syncarpous unilocular gynoecium and later the capsule open.

Geography, cytology. Tropical. Southeast Asia, Malaysia, Australia. X = 11, 23 (or more).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Myrtiflorae (?); Myrtales (? - cf. Lythraceae). Cronquist’s Subclass Dilleniidae; Violales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Cucurbitales.

Species 2. Genera 2; Tetrameles, Octomeles.